1. Field of the Invention
This invention relates to an assembly and method for delivering and deploying an inflation expandable stent, particularly within a lumen of a body vessel. More specifically, this invention relates to the provision of a collar, ring or the like positioned beneath a stent expanding balloon, to be used in conjunction with a cup, positioned at an end portion of the stent, to maintain the stent on the catheter assembly during delivery to a stent deployment site.
2. Description of Relevant Art
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under positive external pressure in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.
A preferred example is the stent described in PCT Application No. 960 3092 A1, published Feb. 8, 1996, the content of which is incorporated herein by reference.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter, without translocating proximally or distally, and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or reduce trauma of the vessel walls.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site. The content of all of these patents is incorporated herein by reference.
A number of inflation expandable stent delivery and deployment assemblies include features interior or exterior to the balloon to aid in positioning the stent during delivery. As described in European Patent Application No. EPO 707 837 A1 to Sheiban, the catheter is provided with concentric rings beneath the balloon. The compressed stent is coaxially mounted on the balloon in the Sheiban assembly, so that the entire length of the stent is between the bulges in the balloon caused by the underlying concentric rings. According to U.S. Pat. No. 4,733,665 (issued with re-examination certificate Jan. 11, 1994), to Palmaz, retainer ring members are disposed on the catheter adjacent (i.e., exterior and external) to the ends of the balloon and adjacent each end of the stent, to retain the stent in its contracted position on the assembly. The retainer ring members can be formed integral with the catheter.
Other patents of interest include U.S. Pat. No. 5,026,377 to Burton et al.; U.S. Pat. No. 5,158,548 to Lau et al.; U.S. Pat. No. 5,242,399 to Lau et al.; U.S. Pat. No. 5,415,664 to Pinchuk, and U.S. Pat. No. 5,453,090 to Martinez et al., all of which are incorporated herein by reference.
According to the present invention, it has now unexpectedly been discovered that, by providing one or two cups to contain one or both ends of the stent, in conjunction with the use of at least one annular collar, axially mounted on the catheter and underneath the balloon, securement of the stent is positively increased, particularly as the cup and collar are placed relatively close to each other. The collar can take any form and may be positioned immediately adjacent the end of the stent, such as opposite to the end of the stent contained by the cup or in a closer position relative to the cup. For example, the collar can also take the form of a mounting ring or cylinder positioned beneath the stent. Further, the collar can take the form of a sheath positioned under the length of the stent. The collar may be at least partially contained within one or both cups so that the stent, along with the intervening balloon, is effectively wedged between the cup and the collar.
The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is xe2x80x9cprior artxe2x80x9d with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. xc2xa71.56(a) exists.
The present invention comprises an assembly for delivery and deployment of an inflation expandable stent. The assembly comprises a catheter having proximal and distal ends. An annular collar or the like is coaxially located on the catheter distal end. A fluid expandable balloon is coaxially mounted over the collar at the catheter distal end. The balloon is expandable from a contracted to an expanded state. A stent is coaxially mounted on the balloon. The stent is inflation expandable from a reduced to an enlarged condition, the reduced condition conforming the stent to the balloon, collar and catheter in the preferred embodiment. The stent has at least an end portion overlying the balloon. At least one cup is coaxially mounted on the catheter distal end. The cup has a first end portion which may overlie the stent end portion. The cup and collar are cooperatively constructed and arranged to retain the stent end portion on the catheter in the stent reduced condition when the balloon is in the contracted state. The balloon and catheter are cooperatively constructed and arranged to cause expansion of the balloon from the contracted to the expanded state to cause enlargement of the stent, including the stent end portion, from the reduced to the enlarged condition, and thereby release the stent end portion from the cup end portion. The cup may be axially spaced from the collar but preferably they are relatively close together. The second end portion of the cup may be fixed to the catheter. The cup may overlie at least a portion of the collar. The collar can be shaped as a single member with the catheter, that is integral with it or the collar may be a separate body mounted axially and positioned on the catheter. The collar may be a mounting ring or cylinder axially positioned between stent end portions under the stent and balloon. The collar may be a sheath under the stent and balloon.
This invention comprises a method for delivering and deploying a stent using the assembly as just described. The method comprises the following steps. A catheter is provided having proximal and distal ends. At least one collar is coaxially mounted at the catheter distal end. A fluid expandable balloon is coaxially mounted over the collar on the catheter distal end. A stent is provided, which is inflation expandable from a reduced to an enlarged condition. The stent, in the reduced condition, is coaxially mounted on the balloon so that at least an end portion of the stent overlies the balloon. At least one cup is provided which has first and second end portions. The cup is in an expanded form, and also has a retracted form. The expanded cup is coaxially mounted on the catheter distal end so that the cup first end portion restrains the stent end portion. The cup first end portion may restrain the stent end portion by overlying the stent end portion. The cup is contracted about the catheter and the stent end portion to fix the stent to the catheter. The cup and collar cooperate to retain the stent in the reduced condition. The assembly is delivered to a deployment site. The balloon is inflated to expand the stent to its enlarged condition, whereby the stent is released from the cup.